Investigation of the Crystal Chemistry of Pb Uranyl Oxide Hydrate Minerals Using a CCD-Based X-Ray Area Detector

[9804723]六价铀（铀酰）矿物在铀矿床的氧化部分中很常见，对于理解铀矿床中的水岩相互作用、锕系元素在环境中的流动性、铀矿和铀尾矿的风化以及地质储存库中乏核燃料的蚀变具有重要意义。本研究将重点研究出现在前寒武纪铀矿床风化部分的氧化铀酰铅水合物矿物，以及利用这类资源产生的风化尾矿中的氧化铀酰铅水合物矿物。这些结构复杂的矿物含有几种不同的铀酰多面体，Pb阳离子和水分子位于层间位置。初步研究表明，这些矿物在某些结构类型中显示出相当大的成分变化，并导致了铀酰多面体片中的阴离子取代可能是允许层间含量变化的电荷平衡机制的假设。利用广泛的晶体学研究、显微探针分析和矿物类似物的合成，将对氧化铀酰矿物范德里石、四辉石、curite、富辉石、sayrite和wlsendorfite进行研究。这些研究将提供这些复杂矿物晶体化学变化的细节。研究结果将用于扩展铀酰矿物的结构层次，并进一步了解这些矿物与其他低温矿物的结构和共生关系。

9804723BurnsHexavalent uranium (uranyl) minerals are common in the oxidized portions of U deposits, and are important for understanding water-rock interactions in U deposits, the mobility of actinides in the environment, the weathering of U mine and mill tailings, and the alteration of spent nuclear fuel in a geological repository. This study will focus on Pb uranyl oxide hydrate minerals that occur in the weathered portions of Precambrian U deposits, as well as in weathered mine tailings that result from the utilization of such resources. These structurally complex minerals contain several different sheets of uranyl polyhedra, with Pb cations and water molecules located in interlayer positions. Preliminary work has demonstrated that these minerals show considerable compositional variability within some of the structure types, and led to the hypothesis that anionic substitution in the sheets of uranyl polyhedra may be the charge-balancing mechanism that permits variation of the interlayer content. The Pb uranyl oxide hydrate minerals vandendriesscheite, fourmarierite, curite, richetite, sayrite, and wlsendorfite will be investigated using extensive crystallographic studies, microprobe analysis, and the synthesis of mineral analogues. These studies will provide the details of the crystal-chemical variability of these complex minerals. The results of the investigations will be used to extend the structural hierarchy of uranyl minerals, and to develop an understanding of the relationship between the structures and paragenesis of these and other low-temperature minerals.